Linear accelerators (LINACs) are useful tools for medical applications, such as radiation therapy and imaging, and industrial applications, such as radiography, cargo inspection and food sterilization. In some of these applications, beams of electrons accelerated by the LINAC are directed at the sample or object of interest for performing a procedure or for analysis. However, in many of these applications, it is preferable to use x-rays to perform the procedure or analysis. These x-rays are generated by directing the electron beams from the LINAC at a x-ray emitting target.
Due to space availability, most medical instruments use standing wave LINACs to accelerate the electrons since standing wave LINACs can be made smaller than traveling wave LINACs. In some medical applications, x-rays of more than one energy band may be desirable for analysis or to perform a procedure. Thus, a LINAC that can be operated to generate alternating outputs of electrons having different average energies is desirable. In theory, x-rays of different energy bands may be generated using electrons with different peak energies. However, the accelerating structure of a standing wave LINAC is generally configured to support only a limited number of allowed modes when the accelerator is operating efficiently, only one of which can accelerate a beam efficiently. It has been difficult to develop an instrument that can operate stably to output electrons at different energies at a sufficiently high dose rate of electrons for the desired applications.
An energy switch is commonly used in medical LINACs for a multi-x-ray energy operation. A mechanical type of energy switch, which comprises a metal plunger actuated by a linear motion actuator, is used in many medical therapy machines. In eight (8) hours of typical operation, if two energies are interleaved, it may be required to activate a switch on the order of 10 million times, which can limit the lifetime of a mechanical switch. An electronic switch can have faster a switching time and a longer expected lifetime than a mechanical switch. However, electronic switches can be prone to overheating during a fast-switching operation of the LINAC.
Systems and methods are disclosed herein for a multi-x-ray energy operation of a LINAC with advantageously low heating of electronic switches.